Recently, the use of non-lethal projectiles for training and recreational purposes in place of conventional bullets has increased. The non-lethal projectiles are often constructed of low-weight, frangible materials that fracture upon impact with the target lessening the momentum transferred by the impact, thereby reducing the likelihood of injury or terminal damage. The projectiles often comprise a polymer material instead of the heavier metal or metal composites used in conventional bullets to reduce the overall weight of the projectile and correspondingly the momentum transferred from the projectile to the target upon impact. The lower weight also allows the projectile to be fired with a reduced propellant charge and travel at a lower speed to further reduce the likelihood of damage to the target. In many applications, a marking fluid or other payload is placed in a space within the projectile such that the marking fluid is dispensed from the projectile upon impact to mark the impact site.
The drawback of using a lightweight projectile is that the lower weight used to reduce the impact energy of the projectile also inherently worsens the ballistic characteristics of the projectile. Specifically, the lower weight reduces the effective range in which the projectile can be fired with reasonable accuracy due to a lower ballistic coefficient than a comparable conventional bullet. A common approach to improving the effective range of the lightweight projectile is to increase the muzzle velocity of the projectile. This increased muzzle velocity compensates for the reduced weight to increase the momentum of the projectile such that the effective range of the projectile increases. However, the increased muzzle velocity creates a standoff distance within which the projectile is travelling sufficiently fast to possibly cause excessive or lethal damage. As a result, compensating for the reduced weight of the projectile by increasing the muzzle velocity of the projectile also increases the standoff distance.
The marking fluid can generally improve the ballistic characteristics of the projectile by filling the hollow interior of the projectile with a liquid medium that increases the overall weight of the projectile. The dissipation of the liquid medium upon impact also provides the dual benefit of reducing the force of the impact. However, if the marking fluid solidifies as a result of excessively high or low temperatures or other storage conditions, the solid projectile can prevent or hinder the fracturing of the projectile thereby reducing the amount of impact energy dissipated by the deformation of the projectile. The solid marking media also impacts with more force than marking fluids as the solid media will not dissipate as readily as marking fluid. Similarly, the storage conditions can cause the marking fluid to separate into solid and liquid phases; or otherwise cause the marking fluid to dry out. The uneven weight of the different phases or a dried out marking fluid can cause unpredictable or poor ballistic characteristics. As non-lethal marking ammunition is often used by the military in places where ideal storage conditions may not be available, the likelihood of the storage conditions having a negative effect on the marking fluid and ultimately the ballistic performance of the projectile is high.
Similarly, spin stabilization is difficult with a liquid filled projectile, as the liquid may not spin at a rate matching or proximate to the spin of the projectile, such that the slower spinning liquid mass moving inside a spinning projectile may cause the projectile rotation to decrease prematurely resulting in an unstable projectile. In addition, any unevenness in the liquid mass can cause the weight of the projectile to shift during flight introducing wobble or otherwise impacting the stability of the projectile. Unstable projectiles rapidly lose velocity leading to decreased range and accuracy.
Moreover, the media needs to be non-toxic and easily removable from clothing such as camouflaged clothing used during training. Ideally, the clothing marked with the marking projectiles could be completely cleaned without the use of heated water or detergents as these may not be readily available.
Lightweight projectiles loaded with marking fluid have significant advantages when used for non-lethal or training purposes. However, the storage limitations of the marking media can reduce the overall effectiveness of the projectile or even increase the likelihood of the injury from using the projectile. There is also a need for a marking media that does not negatively impact the ballistic characteristics of the projectile by changing the weight distribution of the projectile in flight. As such, there is a need for a self-stable marking fluid that can improve the ballistic characteristics of the projectile and maintain proper dispersion upon impact without increasing the likelihood of injury or otherwise causing terminal damage to the target.